The invention relates to improvements in shaft sealing assemblies in which at least two sealing rings within a housing are spaced part from each other and seal against a rotating shaft or against a bush fastened on a rotating shaft, wherein the sealing rings are lubricated by a liquid lubricant in at least one annular chamber between the sealing rings. The invention is applicable particularly to aft-stern tube seals of vessels.
Shaft sealing assemblies of the foregoing type have widespread applications in protecting a rotating shaft-end which emerges from a housing which has to be protected against ingress of moisture, dirt, dust and other contaminants. While innumerable shaft sealing arrangements are known in the prior art ranging from the simplest to those which are very sophisticated, the known sealing arrangements cater to specific requirements and operating conditions and are not universally suitable for all applications. Specifically, while reckoning the functional requirements of shaft seals for aft-stern tube seals of ships, cognizance must be taken of the fact that the seal should function effectively and providing a long life in a very hostile and unfavorable operating environment which includes enormous turbulence of the water in which the ship travels, as also the abrasive particles such as silt or sand and other pollutants or chemicals which might have contaminated the water. The shaft seal for aft-stern applicants should also withstand deleterious vibrations and effects of shaft-eccentricity, without creating a need for frequent and premature replacement of the sealing lubricant within the shaft sealing assembly. Frequent replacements of the shaft sealing lubricant with clean sealing lubricant is cumbersome and uneconomical; besides, any need for frequent lubricant replacement indicates that the shaft seal is letting in ingress of contaminants because of deterioration. The present invention is directed to providing an effective shaft sealing assembly such as for an aft-stern seal of a vessel, to withstand against vibrations and shaft-eccentricity in particular.